Transducers



3 a 0 G3 a 072' R. H. ROBINS TRANSDUCERS United States Patent 3,003,072 TRANSDUCERS Robert Hill Robins, London, England, assignor to United Insulator Company Limited, Chessington, Surrey, England, a British company Filed July 8, 1958, 'Ser. No. 747,249 Claims priority, application Great Britain July 11, 1957 7 Claims. (Cl. 2310-85) This invention relates to electric transducers, more particularly to transducer elements which are intended when immersed in liquid, for example a cleaning liquid, to be energised so as to radiate ultrasonic acoustic energy to assist the cleaning or other action of the liquid on an article immersed therein. Such elements will normally radiate acoustic energy equally from both major surfaces. This is in many cases undesirable. For example radiation from that one of two major surfaces which faces an immersed article to be cleaned is effective but that from the opposite face is relatively inefiective and the energy so radiated represents a waste of input power.

By the present invention I provide an improved ultrasonic transducer element for cleaning or other purposes which permits of a great reduction in the proportion of the total radiated energy which is radiated from one surface and a large increase in the proportion of that total which is radiated from the opposite surface, and yet which has good thermal transmission characteristics so that it will operate without risk of overheating.

In accordance with my invention my improved transducer element has one of its surfaces provided with a porous covering layer consisting of metal or inert inorganic oxide. Preferably the surface, or at least one of the surfaces, provided with the porous layer and the surface, or at least one of the surfaces, free of the porous layer, are major surfaces. Preferably the surface, or at least one of the surfaces, free of the porous layer is highly polished or has a covering layer of glaze.

The porous metal or inert inorganic oxide layer applied in accordance with my invention to a surface of a transducer element provides a substantially permanent means of reducing the radiation of ultrasonic acoustic energy from such surface whilst permitting of a high rate of heat dissipation therefrom, whereby my improved transducer element can operate at a higher power than transducers of the prior art.

In use the transducer is positioned with the surface (hereinafter termed the front surface) which is opposite the surface provided with the porous layer, facing the article to be acoustically radiated. The porous layer of metal or of inert inorganic oxide on the rear surface decreases the radiation from the rear surface without reducing to an undesirable degree the transmission of heat from that surface to the liquid. Polishing or glazing the front surface of the transducer element improves the coupling between it and the liquid and increases the radiation from the front surface as compared with that from a bare unpolished rear surface.

The invention is applicable to transducers of the kind comprising a permanently polarised polycrystalline ceramic piezo-electric body which is provided with electrodes and is intended, when immersed in a cleaning or other liquid, to be energised by the application of an alternating voltage of ultrasonic frequency to radiate acoustic energy to assist the cleaning or other action of the liquid on an article immersed in the liquid. In applying the invention to a transducer of this kind, the electrode of one of the major surfaces is provided with a covering layer consisting of a porous layer of metal or of inert inorganic oxide. Preferably the opposite major surface of the electrode is highly polished or has a covering layer of glaze. The glazed layer may consist of a normal ceramic glaze,

ice

or enamel, which is compatible with the electrode metal and the ceramic body. It is desirable that it should be readily wetted by the liquid in which the transducer is to be immersed.

A porous metal layer may be formed of any metal compatible with the original electrode metal and suitable for application in a manner which will yield a porous layer adherent to the electrode. It may be applied for example by spraying molten metal from a flame spray metallising gun. Preferably a metal of high thermal conductivity is used. In the case of a silver electrode I prefer to use a porous layer of copper.

A porous inert inorganic oxide layer may or may not be formed wholly or in part of an oxide of the metal of which the electrode carrying the porous layer is made. A porous layer of inert inorganic oxide may be applied by a spraying method or any other method which will result in a porous layer which is adherent to the electrode and is of adequate thickness.

The invention is also applicable to transducers of the kind comprising a body of magneto-strictive metallic or ceramic material and intended when immersed in a cleaning or other liquid to be energised by the application of an alternating magnetic field of ultrasonic frequency to radiate acoustic energy to assist the cleaning or other action of the liquid. In applying the invention to a transducer of this kind the rear surface is provided with a porous covering layer consisting of metal or of inert inorganic oxide. The metal or the oxide of this layer may be any metal or metal oxide which is compatible with and adherent to the magneto-strictive metal, or where the magneto-strictive material is ceramic material, adherent to that material. It may be applied by a spraying process. The front face of the transducer, if of metal, may be highly polished; if of ceramic it may be glazed with any normal ceramic glaze or enamel compatible with the ceramic magneto-strictive body.

A preferred form of my improved ultrasonic cleaning element will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is plan view of the cleaning element provided with the covering layer of my invention, and

FIGURE 2 is a sectional view of the element taken on the line IIII of FIGURE 1.

The transducer element 1 comprises a flat rectangular plate 2 of a ceramic material having piezoelectric properties. On one major surface (the front face) is a fired-on coating 3 of silver constituting the major part of one electrode. This part is highly polished or covered with a layer of glaze 4. The remaining part of this electrode 3 extends over one edge of the plate and over a small area of the rear face of the plate. Over the major part of this rear face, but separated from the part of the first electrode 3 thereon is a fired-on coating 5 of silver constituting a second electrode. Over the entire area of this second electrode and over the adjacent part of the first electrode on the rear face is a porous layer 6 of sprayed copper or alumina having a thickness of .005". We have found that when such a transducer element 1 is immersed in liquid and energised by applying between its electrodes 3 and 5 a suitable voltage at a frequency of l mc./s., of the total acoustic energy radiated, about 90% is radiated from the polished front surface and only about 10% from the sprayed rear surface. With an element having a front face of sq. cms. area, energy may be applied to the transducer at the rate of 500 watts without danger of overheating.

What I claim as my invention is:

1. An electric transducer element comprising a body of a material which can be so energised as to generate in the material ultrasonic acoustic energy which radiates from at least two surfaces of said body and, deposited directly onto at least the greater part of one of said surfaces so as to adhere thereto, a porous coating of inorganic material which prevents dissipation into the surrounding medium of a substantial proportion of the energy radiated from said surface.

2. An element as claimed in claim 1 in which the porous coating is a flame-sprayed coating of metal.

3. An element as claimed in claim 1 in which the porous coating is a flame-sprayed coating of an inert inorganic oxide.

4. An electric transducer element comprising a body of piezo-electric material and two electrodes adhering directly to opposite faces of said body and, deposited directly onto at least the greater part of the exposed surface of one of said electrodes so as to adhere thereto, a porous coating which prevents dissipation into the surrounding medium of a substantial proportion of the energy radiated from said surface.

5. An element as claimed in claim 1 in which the energy radiates from two major surfaces one of which carries said porous coating and the other of which is highly polished.

6. An element as claimed in claim 1 in which the energy radiates from two major surfaces one of which carries said porous coating and the other of which is coated with smooth surfaced layer of a glaze.

7. An electric transducer element comprising a body of magneto strictive material, which can be energised to radiate from at least two surfaces and, deposited directly onto at least the greater part of one of said surfaces so as to adhere thereto, a porous coating which prevents dissipation into the surrounding medium of a substantial proportion of the energy radiated from said surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,283,285 Pohlman May 19, 1942 2,447,061 Franklin Aug. 17, 1948 2,520,938 Klein Sept. 5, 1950 2,589,403 Kure Mar. 18, 1952 2,803,129 Bradfield Aug. 20, 1957 2,844,809 Batchelder July 22, 1958 2,892,107 Williams et a1 June 23, 1959 

